I've been fortunate in that my russians have always been OK after hibernation, even when it lasted over 100 days.
I do two things:
1) I soak them. I soak them several times before they go into hibernation to get them fully hydrated and to clean out their bowels. Then I pull them out of hibernation every few weeks, weigh them, and soak them again. This does not interfere with their hibernation - I soak them in cool water for maybe 15 minutes and then I put them right back.
2) I followed the steps in #1 for a couple years, but my torts would still loose about 5% or more of their bodyweight. That's not a big problem, but I was still worried. So then I started to slightly dampen the newspaper substrate in their hibernation box. Very slightly. I figured they were exposed to some humidity when they hibernate underground in the wild, so I would add a little to their otherwise desert-dry surroundings in my very dry basement. They stopped losing so much weight after that.
Of course I live in Missouri with colder winters than you experience. My basement drops below 60F in December and stays their until March. This is sufficient to keep the torts down. If you have warmer weather, the torts may be expending more energy and therefore losing more weight and hydration.
Good luck!
